1. Field of the Invention
This invention relates to gradient tube racks and, more particularly, to a gradient tube rack that is adapted to securely hold gradient tubes while shielding the same against extraneous light while accommodating a high intensity point source of light thereby permitting enhancement of the visibility of a gradient in the gradient tubes.
2. The Prior Art
Numerous qualitative, purification, concentration, and quantitative analysis procedures utilize a gradient tube for determining or otherwise separating phases of slightly different densities. For example, the concentration of a viral sample involves placing a quantity of diluted and "contaminated" liquid with a viral sample dispersed therein in a gradient tube and subjecting the gradient tube, and thereby the sample, to high speed centrifugation. The centrifugation causes a separation and concenration of the various components of the liquid sample according to their respective densities, the heavier density components being toward the base of the gradient tube. The separation usually results in a well-defined gradient which is clearly visible in the gradient tube.
However, it is well-known in the art that it is extremely difficult to observe many purified samples because of the extremely small sample involved and also the relatively small differences in the index of refraction of the various layers within the gradient tube. It has therefore become customary for at least one researcher to fabricate a gradient tube light shield from a cardboard box. The cardboard box is prepared as a shadow box for the gradient tube by orienting the box on its side with the open top toward the researcher. Holes are cut in the top surface of the box with the diameter of the holes being slightly smaller than the diameter of the gradient tubes. The gradient tubes are placed in the cardboard box by being inserted downwardly through the holes with the cardboard edges of the holes frictionally engaging the tubes and thereby suspending the tubes inside the box.
Frequently, the interior of the box is painted with a flat black pait to further enhance visibility of the gradient tubes suspended therein. A light is directed downwardly into the gradient tubes to provide an enhancement of the visibility of the sample or samples within the gradient tube, with the cardboard box blocking extraneous light as a shadow box. However, it is well-known that gradient tubes frequently slip out of the holes and drop into the box with a resulting spillage of the sample contained therein. Not only is valuable researcher time wasted in preparing other samples but sample spillage can also result in unwanted viral and possibly even radioactive contamination.
In addition to providing a visual determination of a sample (or samples) within a gradient tube, the gradient tube may be fabricated from a suitably penetrable plastic material such as a polycarbonate plastic. The plastic permits penetratio with a hypodermic needle at the gradient to withdraw the gradient from the gradient tube through the hollow needle. Furthermore, since the gradient is frequently suspended between an upper and a lower phase of differing densities, it is also customary to puncture the bottom of the tube and allow the contents to drip into a catchment basin thereby removing the lower liquid sample below the gradient into one catchment basin. A change in catchment basins allows the operator to recover the gradient selectively removed thereby from the gradient tube. Either of the foregoing procedures requires a stable platform for supporting the gradient tubes.
An additional procedure involving several gradient samples in different gradient tubes and referred to as equilibrium gradients involves comparing the gradient level in each tube with the gradient level in the adjacent tubes. This procedure is extremely difficult if not impossible to accomplish using the foregoing cardboard box technique.
Various test tube racks and analysis systems are known in the art and the following are references which are known to the inventor:
Seitz, et al (U.S. Pat. No. Des. 231,444) discloses a design for a test tube rack, the rack including vertical slots extending part of the length of any test tubes supported therein.
Dovas (U.S. Pat. No. 2,741,913) discloses a test tube rack fabricated from a solid block of transparent plastic material. Longitudinal slots are formed along the entire length of the tubes holes. A set of graduated scales are placed along one edge of the slots.
Walsh (U.S. Pat. No. 3,109,084) discloses a test tube heater including a test tube holder prepared from a solid block of material and having longitudinal slots formed adjacent the base of the holder.
Kahlenberg (U.S. Pat. No. 3,142,385) discloses a culture tube rack having a plurality of horizontal, parallel plate members with resilient wires mounted to the plates for securing the culture tubes in the rack.
Forrstrom (U.S. Pat. No. 3,186,556) discloses a test tube rack consisting of two hinged sections which fold relative to each other to adapt the test tube rack to be free-standing. Inspection openings are provided adjacent the lower portions of the rack to permit inspection of the tubes.
Auphan, et al (U.S. Pat. No. 3,607,097) discloses an automated analyzer for liquid samples wherein a series of tubes having penetrable walls are carried past a series of needles for penetrating the walls of the tube.
Gulgan, et al (U.S. Pat. No. 3,620,678) dislcoses an automated analysis apparatus for analyzing or otherwise measuring physiological data in biological samples. The samples are encapsulated in a transparent, flexible material and sequentially subjected to the individual laboratory tests on a continuous moving belt.
While the foregoing list of references has come to the attention of the inentor, no representation is made that all of these references may be "prior art" within the meaning of that term under the provisions of 35 USC 102 or 35 USC 103, although these references are disclosed herein so as to fully comply with the duty of candor and good faith as required by 37 CFR 1.56.
In view of the foregoing, it would be a significant advancement in the art to provide a gradient tube rack which securely supports a plurality of gradient tubes while shielding the gradient tubes against extraneous light. It would also be an advancement in the art to provide a gradient tube rack which is supported on a pedestal to permit access underneath the gradient tubes for selectively draining contents therefrom. Such an apparatus and method is disclosed and claimed herein.